Y-chromosomal Adam suddenly got much older

Y-chromosomal Adam suddenly got much older

When Albert Perry was living in slavery in mid-19th century South Carolina, he could not have imagined just how ancient and significant his origins were.  A sample of his Y-chromosome DNA would have shown Albert and his ‘owners’ that here, enslaved in America, was the direct descendant of an African who could rightly be called the ‘father of all mankind.’

This ancient individual passed down his genetic legacy from father to son over 11,000 generations.  In fact, Albert’s ancestor was so old he was probably a member of a different human species to us.

Albert’s ancestor is our ancestor too.  In human genetics, Y-chromosomal Adam is the name given to the most recent common ancestor (MRCA) from whom all living people are descended through the male lines of their family tree.  Up to now, DNA studies had estimated that Y-chromosomal Adam lived between 60,000 and 142,000 years ago.  The discovery that the Y-chromosome of Albert Perry’s ancestor diverged around a staggering 338,000 years ago means that that the Y-chromosomal Adam title now goes to him.

This revelation about the origin of our species came to light when a living descendant of Albert Perry, an African American man living in South Carolina, submitted a DNA sample to the National Geographic Genographic Project.  When none of his genetic markers appeared to match existing Y-DNA haplogroups, the sample was sent to Family Tree DNA for sequencing.  Family Tree DNA’s technicians were equally stumped – this Y chromosome was like none other they had analysed so far.

The sample was then sent to Professor Michael Hammer, a geneticist at the University of Arizona in Tucson, for deeper testing.  He found similarities between the Perry sample and those from 11 West African Mbo men, all living in one village in Cameroon.  They shared a common ancestor as recently as 500 years ago, suggesting that it was also home to Albert Perry’s male ancestors – before they were relocated across the Atlantic by slave traders.

Professor Hammer also confirmed that Albert Perry did not descend from the existing Y-chromosomal Adam and that his lineage diverged from the rest of humanity almost 150,000 years before our species appeared in the fossil record.

What does this mean?  Either anatomically modern humans evolved much earlier than thought, or Perry’s Y chromosome comes directly from a now extinct human species that, at some point within the last 200,000 years, interbred with anatomically modern humans.  This scenario would explain human fossils found in Iwo Eleru, Nigeria in 2011, which showed a strange mix of ancient and modern features.  Professor Hammer said: “The Cameroon village with an unusual genetic signature is right on the border with Nigeria, and Iwo Eleru is not too far away.”

So, thanks to Albert Perry’s descendant and his decision to take a DNA test, we have a new, much older Y-chromosomal Adam, a new Y-DNA Haplogroup – A00 – and further supporting evidence that interbreeding between modern and archaic human species was much more complex than we thought.  How many more surprises are hidden in human DNA around the world?

Sources: University of Arizona and the American Journal of Human Genetics

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Posted by Abroad in the Yard on Friday, 14 August 2015